With the end of this contentious political year finally in sight, we thought it might be a good time to engage in a little constructive bipartisanship. No, we're not going to urge people to support a deserving charity or remind them of all the things we have to be thankful for this Thanksgiving. Instead, we'd like to focus on a topic that we both feel has become unnecessarily partisan and divisive: climate change.

President Barack Obama is greeted by New Jersey Gov. Chris Christie upon his arrival at Atlantic City International Airport on Oct. 31, in Atlantic City, NJ. Obama traveled to the region to take an aerial tour of the Atlantic Coast in New Jersey in areas damaged by Superstorm Sandy. Pablo Martinez Monsivais/Associated Press

The two of us belong to different parties and generally support different political candidates. One of us heads an environmental foundation, the other an economic development agency. Our political philosophies and visions of a better future are clearly distinct, although not necessarily incompatible.

Despite these differences, we are both convinced by the evidence that the science underpinning climate change is compelling; that climate change is occurring; that human activity is the primary cause; that it represents a real and present danger to us; and that we are running out of time to deal with this problem effectively.

We understand that not everyone shares these views, and that's OK. Among the values we share with most Americans is the belief that free and open debate is not only a foundational principle of our society, but is also indispensable to any productive discussion and successful resolution of difficult problems.

But "believing" in global warming is not like believing in reincarnation or original sin. It's not even like believing in states' rights or the progressive income tax. There are many subjects on which one person's beliefs and opinions are just as good as anyone else's. The science of climate change is not one of those subjects. It is either a scientific reality or it is not. Our personal preferences or opinions are irrelevant. Debate over global warming has to be based on scientific evidence and the scientific method.

For that reason, climate change shouldn't be a partisan issue. There's no such thing as Republican or Democratic science. Why then should Republicans and Democrats be divided along party lines on the scientific question of whether climate change is real and what's causing it? It would be like the parties dividing over whether flu is caused by a virus, or the tides, by the moon's gravitational pull.

Many Republicans seem to resist the science of climate change because they distrust environmentalists or find the steps proposed to combat global warming unpalatable. Many Democrats appear to embrace it because the resulting policy prescriptions -- conservation, alternative energy and reduced consumerism -- are agendas they were pushing already.

We are not among those who believe that the science of climate change is "settled" and that further debate should be stifled. The history of scientific discovery is rife with examples of well-established theories being altered and even disproved. But the debate should be based on science, not partisan strategies or conspiracy theories on either side.

We also recognize that serious policy disagreements remain as to the best remedies even among those who are convinced that the climate threat is real. But time is not on our side. Greenhouse gases accumulate in the atmosphere over decades and dissipate slowly. Their expected impacts are often lagging but persist for decades thereafter. If the science is right, 20 years from now the problem will be immeasurably greater and the remedies far more difficult and costly.

Whether you "believe" climate change is a certainty or just 90 percent or 70 percent or even 50 percent likely, the risk is too great to postpone acting. So while the scientific debate should remain free to continue, we believe that the policy debate needs to move to center stage. Should we concentrate primarily on replacing coal plants with renewable energy and conservation, or new nuclear plant designs? How big a bet should we place on research into new technologies or on diplomacy and international agreements? What about a carbon tax? Since none of these approaches is mutually exclusive, the range of alternatives to consider and the mix of policies available seem almost limitless.

Between the two of us there are significant differences on the most effective and appropriate responses. What is most needed now is a robust debate over how to address this challenge, not inaction based on denial of the evidence.

In a sense, this is like the debate over the federal deficit. There are legitimate differences of opinion over whether the appropriate response to the deficit is to raise taxes, cut spending, stimulate growth or a mix of these. Advocates of each of these positions have something to contribute to the debate. Those who simply ask "What deficit?" do not.

Jack Roberts is a Eugene businessman and former Oregon labor commissioner. Angus Duncan is president of the Bonneville Environmental Foundation and chairman of the Oregon Global Warming Commission.